Temperature increase abolishes ability of turtle olfactory receptors to discriminate similar odorant

We examined the effects of temperature changes on odor-discriminating ability of turtle olfactory receptors in vivo by applying the cross-adaptation method to the olfactory bulbar responses. The olfactory system discriminated well all eight pairs of odorants examined at 5 and 18 degrees C. The ability of the olfactory receptors to discriminate pairs of odorants having similar structures (e.g., trans-3-hexenol and cis-3-hexenol; d-carvone and l-carvone) was reversibly abolished by increasing the temperature up to 40 degrees C, whereas discrimination of odorants having quite different structures was much less affected. The membrane fluidity of cells isolated from turtle olfactory epithelia and liposomes made of lipids extracted from the epithelia changed in a similar temperature range as for the decrease of the odor-discriminating ability, suggesting that an increase in membrane fluidity is correlated with the abolishment of the odor-discriminating ability. The present results also suggest that in vivo desensitization (adaptation) occurs not at the cellular level but at the receptor level. This mechanism was supported by the data recorded from a single olfactory cilium, showing that a single cell has both receptors for l-carvone and d-carvone and that the response to d-carvone appeared after the response to l-carvone was adapted.